DENVER -- The Nationals' attempt to keep a rally alive with a second-inning challenge came up empty Tuesday.

Bryce Harper, who drew a two-out walk, attempted to reach third from first on Ian Desmond's single up the middle. But Charlie Blackmon fielded the ball cleanly and fired to third from center field, and third baseman Nolan Arenado applied the tag ahead of a head-first-sliding Harper.